The present invention relates to an automatic freeze protection valve for fluids under pressure and especially to a freeze protection valve for solar heaters to prevent the freezing of liquids in solar panels and the like.
In the past, solar water heating systems have a roof mounted collector panel which includes headers or manifolds and a plurality of tubes extending between the headers or a single tube applied in a coiled or serpentine fashion. This collector panel is connected by piping to a storage tank and includes means to move the solar heated water from the panel to the tank.
The prior art freeze protection valves include those that isolate the solar panel and then drain the water within it upon the valve reaching a predetermined temperature. Other freeze protection valves isolate the collector panel and then drain the water back into a container or tank section designed for capturing the water. This type of valve is commonly electrically actuated.
Another type of valve is one that utilizes a wax plug or freon under pressure from within the valve to activate the valve opening to flush water through the panel and piping and then to dispell it outside of the solar water heating system. The flushing water from the residential or commercial plumbing system typically has a temperature of 50 to 65 degrees fahrenheit and thus warms the panel and plumbing above freezing. Such valves commonly open when their temperature falls to 42 to 43 degrees fahrenheit and close when their temperature rises to 43 and 45 degrees fahrenheit. The prior art freeze protection valves sense the temperature of their activating fluid from within the valve itself, either at the inlet or at the lower portion of the valve. These valves, by design, either measure collector inlet or outlet fluid temperature or ambient temperature. Under freeze conditions, however, the coldest portion of the absorber panel experiences temperatures typically 10 to 15 degrees fahrenheit colder than ambient, and 8 to 10 degrees colder than inlet or outlet connections due to the evening sky radiation heat loss. Under some conditions these temperature differences can be much greater. Because this temperature difference is not sensed, conventional valves may allow portions of the absorber panel to freeze before they begin to purge fluid. This freezing thus defeats the freeze protection purpose of the valve. At other times, conditions such as cloudy skies and windy, will cause the ambient temperature to drop to approximately 40 degrees fahrenheit and the panel absorber will also be at 40 degrees fahrenheit and not in jeopardy of freezing. Prior art freeze protection valves sensing temperatures below their set points will purge the panel dumping water unnecessarily under these conditions.
Typical prior art purge valves provide a modulating flow of purging fluid dependent upon temperature. As the temperature drops to their point of actuation the valves allow a small trickle of flow to begin. The temperature continues to decrease, they increase the purging flow. Such a modulated flow would appear beneficial as it would minimize the amount of water purged and in fact does minimize this flow of water and works well for serpentine or coil type collectors. However, the majority of collectors installed presently are of the header type. Such a modulated flow and the low flow first introduced allow flow patterns to develop within the panel absorber itself such that some riser tubes receive a greater flow of liquid than others. It is a common occurrence that even with prior art freeze protection valves actuated to purge, some panel risers which are starved for purge flow, do freeze, defeating the purpose of the valve.
Freeze protection valves have also used wax or freon to activate the valve. These valves may reach temperatures from 300 to 400 degrees fahrenheit under panel stagnation. Such high temperature cycling tends to cause a change in the activation temperature of the wax valves and a leakage of the freon in the freon valves which leads to valves that will activate more often than necessary.
______________________________________ INVENTOR U.S. PAT. NO. ______________________________________ B. OQUIDAM 4,309,982 E. F. DUVAL 4,280,478 D. J. KAZIMIR 4,453,534 M. F. SCHOENHEIMER 4,454,890 ANDRE BONNET 4,368,724 L. A. KOLZE 4,460,006 W. B. NOLAND 3,480,027 F. DONNELLY 4,457,326 W. R. WALTERS 3,642,015 ______________________________________
The present invention contemplates a new and improved freeze protection valve which activates based on absorber panel temperature and is unaffected by the ambient or fluid temperature flowing through it, thus allowing for a lower set point and less unnecessary cycling. The present valve utilizes an activating material, such as mercury, which provides better resistance and longevity to affect the temperature cycles, and a valve which is designated to open fully upon activation temperature, providing maximum purge flow rather than modulating the flow.